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(Wurtemburg, current Germany, 1571-Regensburg, ID, 1630) Astronomer, mathematician, and German physicist. Son of a mercenary - who served for money in the army of the Duke of Alba and disappeared into exile in 1589 - and of a mother suspected of practising sorcery, Johannes Kepler was the aftermath of a sordid and miserable childhood thanks to his tenacity and intelligence.
After studying in seminaries of Adelberg and Maulbronn, Kepler joined the University of Tübingen (1588), where he studied theology and was also a disciple of the Copernican Michael Mästlin. In 1594, however, he interrupted his theological career by accepting a position as Professor of mathematics at the Protestant Seminary in Graz.
Four years later, a few months after contracting a marriage of convenience, the edict of Archduke Ferdinand against Protestant teachers forced him to leave Austria and moved to Prague in 1600 invited by Tycho Brahe. When this died suddenly the following year, is replaced by Kepler as mathematician Rodolfo II imperial, with the custom finish astronomical tables initiated by Brahe and quality of astrological counselor, function which frequently resorted to earning a living.
Died in 1611 his wife and one of his three sons; shortly afterwards, after the death of the Emperor and the ascent to the throne of his brother Matías, he was appointed Professor of mathematics at Linz. There resided Kepler until, in 1626, the economic difficulties and the climate of instability caused by the thirty years war brought it to Ulm, where he oversaw the printing of the tables rudolphine, initiated by Brahe and completed in 1624 by himself using the laws concerning the planetary motions that he established.
In 1628, he joined the service of A. von Wallenstein, in Sagan (Silesia), who promised him, in vain, to compensate him for the debt owed to it by the Crown over the years. A month before his death, victim of the fever, Kepler had left Silesia in search of a new job.
The first stage in the work of Kepler, developed during his years in Graz, focused on the problems associated with the planetary orbits, as well as variable speeds with the planets through them for what came from the Pythagorean conception according to which the world is governed on the basis of a pre-established harmony. After trying to an arithmetic solution of the issue, thought he found a geometric response relating the intervals between the orbits of the six planets then known as the five regular solids. He judged to have thus resolved a "cosmografico mystery" which he exhibited in his first work, Mysterium cosmographicum (cosmografico mystery, 1596), which sent a copy to Brahe and other to Galileo, which maintained a sporadic epistolary relationship and who joined in the Copernican advocacy.
During the time he remained in Prague, Kepler did a remarkable job in the field of Optics: it stated a first satisfactory approximation of the law of refraction, distinguished for the first time clearly between the physical problems of vision and its physiological aspects, and analyzed the geometrical aspect of various optical systems.
But the most important work of Kepler was the revision of the cosmological diagrams known from the vast amount of points accumulated by Brahe (in particular, those relating to Mars), work which led to the publication, in 1609, of the astronomy nova (new astronomy), the work containing two first called Kepler's laws, relating to the ellipticity of the orbit and the equality of the swept areas , in equal times, by vectors rays that unite the planets with the Sun.
Culminated his work during their stay in Linz, where he enunciated the third of its laws, which numerically related periods of revolution of the planets with their middle Sun distances; published in 1619 in you Harmonices mundi (on the harmony of the world), as one of the harmonies of nature, whose secret believed to have managed to reveal thanks to a peculiar synthesis of astronomy, music, and geometry.